In the production of integrated circuit devices, a lithographic process utilizing near ultraviolet radiation (e.g., I-line) has been generally performed. However, it is considered to be very difficult to implement sub-quarter-micron microfabrication using near ultraviolet radiation. Specifically, it is difficult to achieve a higher degree of integration utilizing near ultraviolet radiation. Therefore, a lithographic process that can implement microfabrication with a line width of 0.20 μm or less has been desired in order to achieve a higher degree of integration.
As a means that enables such microfabrication, a lithographic process utilizing radiation having a wavelength shorter than that of near ultraviolet radiation has been studied. Examples of radiation having such a short wavelength include deep ultraviolet radiation (e.g., a bright-line spectrum of a mercury lamp and radiation emitted from an excimer laser), X-rays, electron beams, and the like. Among these, radiation emitted from a KrF excimer laser (wavelength: 248 nm), an ArF excimer laser (wavelength: 193 nm), or an F2 excimer laser (wavelength: 157 nm), EUV radiation (e.g., wavelength: 13 nm), electron beams, and the like have attracted attention.
Along with the use of short-wavelength radiation, a number of radiation-sensitive resin compositions suitable for use with short-wavelength radiation have been proposed. For example, a composition that utilizes a chemical amplification effect due to a component having an acid-dissociable functional group and a radiation-sensitive acid generator (hereinafter may be referred to as “chemically-amplified radiation-sensitive composition”); said composition generating an acid upon exposure to radiation (hereinafter may be referred to as “exposure”) has been proposed.
Specifically, a composition that contains a polymer having a t-butyl ester group of a carboxylic acid or a t-butyl carbonate group of phenol and a radiation-sensitive acid generator has been proposed (see Patent Document 1). According to this composition, the t-butyl ester group or the t-butyl carbonate group contained in the polymer dissociates due to the action of an acid generated upon exposure and forms an acidic group that is a carboxyl group or a phenolic hydroxyl group. Therefore, the exposed area of the resist film formed of the composition is easily dissolved in an alkaline developer. Accordingly, a desired resist pattern can be formed on the resist film by developing the resist film using an alkaline developer.
The radiation-sensitive acid generator contained in the chemically-amplified radiation-sensitive composition must have a high radiation transmittance and a high quantum yield when generating an acid. The acid generated by the radiation-sensitive acid generator must have sufficiently high acidity, a sufficiently high boiling point, and an appropriate diffusion length in the resist film, for example.
In order to ensure that the acid has high acidity, a sufficiently high boiling point, and an appropriate diffusion length, the structure of an anion moiety is important when using an ionic radiation-sensitive acid generator. Moreover, when a nonionic radiation-sensitive acid generator having a sulfonyl structure or a sulfonate structure is used, the structure of the sulfonyl moiety is important.
For example, a radiation-sensitive acid generator having a trifluoromethanesulfonyl structure generates an acid having sufficiently high acidity so that the photoresist exhibits a sufficiently high resolution. However, such a radiation-sensitive acid generator has a drawback in that the photoresist shows high mask dependence since the acid generated by the radiation-sensitive acid generator has a low boiling point and an inadequate diffusion length; i.e., a large diffusion length of the acid. Further, a radiation-sensitive acid generator having a sulfonyl structure (e.g., 10-camphorsulfonyl structure) bonded to a large organic group since the acid generated by the radiation-sensitive acid generator has a sufficiently high boiling point and an adequate diffusion length. That is, it shows reduced mask dependence due to a sufficiently short diffusion length. However, the photoresist exhibits an insufficient resolution since the acid has insufficient acidity.
Here, a radiation-sensitive acid generator having a perfluoroalkylsulfonyl structure (e.g., perfluoro-n-octanesulfonate (PFOS)) has attracted attention in recent years due to the capability of generating an acid having sufficiently high acidity, a sufficiently high boiling point, and an appropriate diffusion length.
However, since a radiation-sensitive acid generator having a perfluoroalkylsulfonyl structure (e.g., PFOS) is considered to cause environmental problems due to low combustibility and potential problem associated with its accumulation in human body, it is not free from a problem that the U.S. Environmental Protection Agency has proposed a rule regulating the use of these compounds (see Non-patent Document 1).
On the other hand, since it becomes necessary to more accurately control the line width, for example, if the design device dimensions are sub-half-micron or less, it is important for the chemically-amplified resist to have a high resolution and form a resist pattern having excellent surface smoothness. When a chemically-amplified resist cannot form a resist pattern having excellent surface smoothness, elevations or depressions (hereinafter may be referred to as “nano-edge roughness”) on the surface of the film are transferred to the substrate when transferring the resist pattern by etching or the like. As a result, the dimensional accuracy of the pattern deteriorates. Therefore, it has been reported that the electrical properties of the resulting device may be impaired (see Non-patent Documents 2 to 5, for example).    Patent Document 1: JP-B-2-27660    Non-patent Document 1: Perfluorooctyl Sulfonates; Proposed Significant New Use Rule    Non-patent Document 2: J. Photopolym. Sci. Tech., p. 571 (1998)    Non-patent Document 3: Proc. SPIE, Vol. 3333, p. 313    Non-patent Document 4: Proc. SPIE, Vol. 3333, p. 634    Non-patent Document 5: J. Vac. Sci. Technol. B16 (1), p. 69 (1998)